All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we congratulate you upon embracing Islam and we ask Allaah to make you firm and steadfast on this religion until the day you meet Him. Also, we ask Him to bless you with religious knowledge.
As regards calling Allaah a father, meaning a spiritual father, then this is not permissible for many reasons.
1) The Names and Attributes of Allaah are restricted to texts [in the Quran or authentic Sunnah], and we can only name Him by what He named Himself in His Book or by what the Prophet , named Him with in his Sunnah. Naming Allaah with names that He did not name Himself with or that the Prophet did not name Him with is considered as a deviation in Allaah's Names and Attributes. Allaah Says (what means): {And (all) the most beautiful Names belong to Allaah, so call on Him by them, And leave [the company of] those who practice deviation concerning His names. They will be recompensed for what they have been doing.} [Quran 7:180]
2) Calling Allaah a spiritual father is an imitation of the Christians and the Prophet forbade us from imitating them as he said: "He is not one of us he who imitates non-Muslims. Do not imitate the Jews and the Christians." [At-Tirmithi] However, it is permissible to call the Prophet a spiritual father because Allaah Says (what means): {The Prophet is more worthy of the believers than themselves, and his wives are their (believers') mothers.} [Quran 33:6] Ibn 'Abbaas and his father, recited this as: {The Prophet is more worthy of the believers than themselves, and he is their father, and his wives are their (believers') mothers} and this is according to the copy of the Quran written down by Ubay Ibn Ka'b . Indeed it is confirmed that the Prophet said: "I am like a father for you, I teach you [that which you do not know]." [Abu-Daawood]
As regards the saying of Allaah (which means): {Muhammad, (), is not the father of any man among you…} [Quran 33:40] What is meant in this verse is the biological father. Al-Qurtubi said, "The correct opinion is that it is permissible to name the Prophet as the father of the believers, meaning by respect." He further added, "Although he is their father in terms of glorification and exaltation."
As regards the brotherhood that exists among the Muslims, it is the brotherhood in religion and faith as Allaah Says (what means): {The believers are nothing else than brothers (in Islamic religion).} [Quran 49:10]
Allaah Knows best.